Abstract: A method is provided for establishing a communication path in an optical network, the communication path comprising a plurality of sections, wherein the power level of a section is controlled by a respective power control unit of a network node. The method comprises the steps of, in response to a request to establish a communication path, step 201, controlling at least one power control unit to perform a first power-up mode of operation. The first power-up mode of operation comprises the step of setting a power control factor of a respective section of the communication path directly to a value estimated to provide a target power level, step 203.

Abstract: Apparatus (10) for an optical communications network has optical paths for optical traffic, and optical ports (20,40), one of which is an unused input port (20). A security monitoring system (30) has a blocking part (50) comprising an interface (51) coupled removably to the unused input port (20) to occupy it to prevent unauthorized access. A light source is optically coupled to the interface (51) such that, when the interface is coupled to the unused input port, light can be transmitted through the interface (51) into the unused input port (20). An optical detector (60) can detect light reflected back from the interface (51), and there is alarm circuitry (70) configured to output an alarm signal based on the detecting of the reflected light. This monitoring can help make the node more secure from interference such as the introduction of a noise signal. The system can be passive or active, and does not require a change in the installed node configuration and so can be added easily to existing infrastructure.

Abstract: A method (10) of changing operating mode of an optical amplifier in an amplifier chain in an optical network, the optical amplifier initially configured to operate in a first mode to apply a substantially constant first gain to an optical signal comprising a plurality of optical channels, the method comprising, after a time period unique to the optical amplifier within the amplifier chain (12), configuring the optical amplifier to operate in a second mode to apply a second gain to the optical signal so that the optical power of the optical signal is maintained at a target optical power dependent on a current plurality of optical channels in the optical signal (14).

Abstract: A method (10) of controlling optical signal power levelling in an optical communication network node configured to apply an optical attenuation, ?, to a pass-through optical signal. The method comprises: a. performing the following steps i. to iii. until an attenuation variation value, ??, is greater than a preselected attenuation variation threshold value (18), ??TH: i. measuring (12) an optical signal power of an optical signal; ii. calculating (14) a difference, ?P, between the measured optical signal power and a target optical signal power; iii. calculating (16) a value for the attenuation variation, ??, to be applied to the optical attenuation taking account of ?P; b. obtaining (20) a current value of the optical attenuation, ?n, and obtaining (22) a new optical attenuation value, ?n+1, in dependence on the current value of the optical attenuation, a current value of the attenuation variation, ??n, and at least an earlier value of the attenuation variation, ??n?1; and c.

Abstract: Apparatus for an optical communications network has optical paths for optical traffic, and optical ports, one of which is an unused output port. A security monitoring system has a blocking part coupled removably to the unused output port to occupy it to prevent unauthorized access. An optical detector can detect optical signals passing through the unused output port to the blocking part, and there is alarm circuitry configured to output an alarm signal based on the detecting of the optical signals. This monitoring can help make the node more secure from interference or from eavesdropping. By blocking the port, the monitoring can be independent of the type of signals on the optical paths. The system can be passive or active, and does not require a change in the installed node configuration and so can be added easily to existing infrastructure.

Abstract: A method is provided for establishing a communication path in an optical network, the communication path comprising a plurality of sections, wherein the power level of a section is controlled by a respective power control unit of a network node. The method comprises the steps of in response to a request to establish a communication path, step 201, controlling at least one power control unit to perform a first power-up mode of operation. The first power-up mode of operation comprises the step of setting a power control factor of a respective section of the communication path directly to a value estimated to provide a target power level, step 203.

Abstract: A method (10) of changing operating mode of an optical amplifier in an amplifier chain in an optical network, the optical amplifier initially configured to operate in a first mode to apply a substantially constant first gain to an optical signal comprising a plurality of optical channels, the method comprising, after a time period unique to the optical amplifier within the amplifier chain (12), configuring the optical amplifier to operate in a second mode to apply a second gain to the optical signal so that the optical power of the optical signal is maintained at a target optical power dependent on a current plurality of optical channels in the optical signal (14).

Abstract: Apparatus (10) for an optical communications network has optical paths for optical traffic, and optical ports (20,40), one of which is an unused input port (20). A security monitoring system (30) has a blocking part (50) comprising an interface (51) coupled removably to the unused input port (20) to occupy it to prevent unauthorised access. A light source is optically coupled to the interface(51) such that, when the interface is coupled to the unused input port, light can be transmitted through the interface (51) into the unused input port (20). An optical detector (60) can detect light reflected back from the interface (51), and there is alarm circuitry (70) configured to output an alarm signal based on the detecting of the reflected light. This monitoring can help make the node more secure from interference such as the introduction of a noise signal. The system can be passive or active, and does not require a change in the installed node configuration and so can be added easily to existing infrastructure.

Abstract: A method (10) of controlling optical signal power levelling in an optical communication network node configured to apply an optical attenuation, ?, to a pass-through optical signal. The method comprises: a. performing the following steps i. to iii. until an attenuation variation value, ??, is greater than a preselected attenuation variation threshold value (18), ??TH: i. measuring (12) an optical signal power of an optical signal; ii. calculating (14) a difference, ?P, between the measured optical signal power and a target optical signal power; iii. calculating (16) a value for the attenuation variation, ??, to be applied to the optical attenuation taking account of ?P; b. obtaining (20) a current value of the optical attenuation, ?n, and obtaining (22) a new optical attenuation value, ?n+1, in dependence on the current value of the optical attenuation, a current value of the attenuation variation, ??n, and at least an earlier value of the attenuation variation, ??n?1; and c.

Abstract: Apparatus for an optical communications network has optical paths for optical traffic, and optical ports, one of which is an unused output port. A security monitoring system has a blocking part coupled removably to the unused output port to occupy it to prevent unauthorised access. An optical detector can detect optical signals passing through the unused output port to the blocking part, and there is alarm circuitry configured to output an alarm signal based on the detecting of the optical signals. This monitoring can help make the node more secure from interference or from eavesdropping. By blocking the port, the monitoring can be independent of the type of signals on the optical paths. The system can be passive or active, and does not require a change in the installed node configuration and so can be added easily to existing infrastructure.

Abstract: An optical demultiplexing structure and method for demultiplexing channels from a wavelength multiplexed optical signal comprising a first optical filter (115), a second optical filter (117), and at least one third optical filter (120), wherein the first filter has a band-pass characteristic for extracting a first set of channels from the optical signal, and the second filter has a cut-off wavelength corresponding to a wavelength within the pass-band of the first filter, and wherein the first filter is connected to the second filter, the second filter extracting a second set of channels from the channels that remain after extraction of first the set of channels by the first filter, and wherein the at least one third filter has a passband to extract a subset of channels from the second set of channels spaced apart from the first set of channels. The corresponding multiplexing structure and method are also described.

Abstract: An optical demultiplexing structure and method for demultiplexing channels from a wavelength multiplexed optical signal comprising a first optical filter (115), a second optical filter (117), and at least one third optical filter (120), wherein the first filter has a band-pass characteristic for extracting a first set of channels from the optical signal, and the second filter has a cut-off wavelength corresponding to a wavelength within the pass-band of the first filter, and wherein the first filter is connected to the second filter, the second filter extracting a second set of channels from the channels that remain after extraction of first the set of channels by the first filter, and wherein the at least one third filter has a passband to extract a subset of channels from the second set of channels spaced apart from the first set of channels. The corresponding multiplexing structure and method are also described.

Abstract: In an optical add/drop amplification device (1) arranged between fibre spans (2, 3) in an optical telecommunications system, comprising a first input amplifier (4), a channel add/drop device (7) and an output amplifier (8) connected in a series path, the input amplifier (4) is arranged to produce substantially constant output power, such that the output power of amplified spontaneous emission (ASE) noise compensates in use for loss of signal power in the event of breakage of a fibre span, to ensure survival of any channels added at the add/drop device. In accordance with the invention, an additional input amplifier (9) is provided to produce the compensating ASE noise in the event of failure of the first input amplifier.